This invention relates to vacuum cleaners and more particularly to an indicator for detecting when the dirt collecting filter bag is substantially full and should be replaced.
During the operation of a vacuum cleaner, dirt laden air is drawn into the cleaner inlet, directed through a dirt collecting filter bag and clean filtered air is exhausted through an outlet. The added friction due to the dirt that collects in the bag results in a reduction in the air flowing through the cleaner and an increase in the pressure drop through the bag. When the pressure drop reaches a predetermined amount, the bag has separated and collected all that it practicably should. Thereafter, continued operation with the same bag will cause so great a pressure drop that the air flow and suction does not provide good cleaning. Moreover, increased power is required to drive the cleaner motor-blower with a substantially full bag. Another effect of operating with the bag in such condition is that most canister vacuum cleaner motor blowers are of the direct flow type whereby the filtered air is thereafter used to cool the motor. When the air flow drops the temperature of the motor increases and can eventually destroy the motor.
This problem has been recognized and many attempts at a solution have been made. Cawl U.S. Pat. No. 2,741,328; Forsberg U.S. Pat. No. 2,192,224; Martinet U.S. Pat. No. 2,203,171; and Sellers U.S. Pat. No. 2,117,368 are indicative of some of the approaches in indicating when the bag is substantially full.